Field of the Invention
The present invention relates to pneumatic tires.
Description of the Related Art
To date, it has been known that rolling resistance of tires adversely affects running performance and fuel consumption rate of vehicles, and the like. Causes of rolling resistance include: resistance due to hysteresis loss caused by repeated deformation of tire components formed of rubbers and/or cords; air resistance; frictional resistance between a road surface and the tire; and the like, and these resistances are caused by rotation of the tire. Among them, resistance due to hysteresis loss in tire components, is a main cause.
Therefore, various measures to reduce rolling resistance of tires have been taken to date. As one of these measures, a method has been known in which a rubber having a relatively low energy loss is used for a tread that is greatly deformed during running and that has used therein an increased amount of rubber. However, in this method, grip performance of the tire may be deteriorated. In particular, a problem arises that wet grip performance may be deteriorated.
Another method is known in which a height of a flange of a rim to be used is reduced. In this method, in a state where a tire is mounted to the rim, a deformed region of sidewalls is increased, thereby restraining deformation behavior of a tread region. However, in order to use this method, a flange portion of the rim needs to be formed in a particular shape. Therefore, a problem arises that it is difficult to diffuse such products in the market.
A method is also known in which an internal pressure of a tire is set so as to be higher than usual, to reduce deformation of the tire under load. However, in this method, a stiffness constant of the tire is increased, and attenuation of vibration thus becomes poor, so that ride comfort may be deteriorated.
In JP57-87704, it is indicated that internal loss due to repeated bending deformation of a belt around a tire equator, exerts a great influence on rolling resistance of the tire, and the internal loss can be reduced when a shape of a tread surface and a shape of a disposed belt satisfy a specific relationship. In this technique, as a parameter concerning a tire configuration that exerts an influence on rolling resistance, depressed dimensions (displacements in the radially inward direction) of a top position of the tread surface and a top position of a belt surface, in the tire under load, are used. In this technique, alignment over a wide range in the tire is not considered.
Further, in JP06-199105, a radial tire configured to restrain uneven wear in shoulder portions of a tread, is suggested. The configuration of this tire is defined by a relationship among a displacement (may be referred to as a degree of camber) of a tread surface in a radially inward direction of the tire, a displacement of a belt in the radially inward direction of the tire, a displacement of a carcass in the radially inward direction of the tire, and a size of an effective region of the belt in a belt width direction, in a predetermined range near outer ends in the belt width direction. However, alignment over a wide range in the tire is not also considered in this technique.